Some engine systems may include devices such as throttle turbine generators to use energy from a pressure difference across a throttle that is otherwise wasted in an intake passage of an engine. In some examples, the throttle turbine generator includes a turbine mechanically coupled to a generator which may generate current that is supplied to a battery of the engine. By charging the battery with such a generator, fuel economy of the engine system may be improved, as compared to charging the battery with an engine driven generator.
During transient operating conditions, however, when the throttle turbine generator is used, airflow changes to the engine may be slowed down or delayed, due to rotational inertia of the turbine. As such, engine operating efficiency and/or exhaust emissions and/or drivability may be degraded, due to changes in various operating parameters such as air fuel ratio and torque, because of the slowed or delayed changes in airflow to the engine.
The inventors herein have recognized the above problem and have devised an approach to at least partially address it. Thus, a method for an engine system with a throttle bypass around a throttle disposed in an intake passage of the engine system is disclosed. The throttle bypass includes a turbine in communication with an auxiliary generator. In one example, the method comprises adjusting an operating parameter based on airflow to cylinders of an engine during a transient operating condition.
In such an approach, airflow to cylinders of the engine is measured such that airflow to the cylinders is known during the transient operating condition. As such, one or more engine operating parameters may be adjusted to compensate for the slowed or delayed airflow. As an example, fuel injection timing and/or fuel injection amount may be adjusted to compensate for the slowed or delayed airflow. For example, fuel injection timing may be retarded and/or fuel injection amount may be adjusted such that the air fuel ratio is maintained. In this manner, engine operating efficiency and exhaust emissions may be maintained or improved during transient operating conditions. In another example, throttle opening may be adjusted such that the desired airflow to the engine is maintained during transient conditions. In this manner, engine drivability may be maintained or improved during transient operating conditions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.